ceph: fix potential bad pointer deref in async dirops cb's

The new async dirops callback routines can pass ERR_PTR values to
ceph_mdsc_free_path, which could cause an oops. Make ceph_mdsc_free_path
ignore ERR_PTR values. Also, ensure that the pr_warn messages look sane
even if ceph_mdsc_build_path fails.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJeff Layton <jlayton@kernel.org>
Reviewed-by: NIlya Dryomov <idryomov@gmail.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

fs/ceph/dir.c

@@ -1051,8 +1051,8 @@ static void ceph_async_unlink_cb(struct ceph_mds_client *mdsc,
 
 	/* If op failed, mark everyone involved for errors */
 	if (result) {
-		int pathlen;
-		u64 base;
+		int pathlen = 0;
+		u64 base = 0;
 		char *path = ceph_mdsc_build_path(req->r_dentry, &pathlen,
 						  &base, 0);
 

fs/ceph/file.c

@@ -527,8 +527,8 @@ static void ceph_async_create_cb(struct ceph_mds_client *mdsc,
 
 	if (result) {
 		struct dentry *dentry = req->r_dentry;
-		int pathlen;
-		u64 base;
+		int pathlen = 0;
+		u64 base = 0;
 		char *path = ceph_mdsc_build_path(req->r_dentry, &pathlen,
 						  &base, 0);
 

fs/ceph/mds_client.h

@@ -521,7 +521,7 @@ extern void ceph_mdsc_pre_umount(struct ceph_mds_client *mdsc);
 
 static inline void ceph_mdsc_free_path(char *path, int len)
 {
-	if (path)
+	if (!IS_ERR_OR_NULL(path))
 		__putname(path - (PATH_MAX - 1 - len));
 }